/Engine/Source/Runtime/Renderer/Public/MeshPassProcessor.h
When ID table is frozen, items with a zero ref count aren't actually released, so if the same item gets used again, its ID doesn't change. Useful when re-creating draw commands in the middle of the frame, where you want to prevent existing pipeline state IDs from changing, which may be referenced by in flight tasks. Unfreezing the table will clean up anything with a zero ref count.
static void FreezeIdTable ( bool bEnable )